Extreme Rainfall Across the Pikes Peak Region 9/10-13, 2013

The rainfall episode of September 10th through 13th, 2013 taught us some valuable lessons with regard to how watersheds across the Pikes Peak Region can handle runoff. 

Those with hydrology expertise will assess the rarity of such an episode with regard to rainfall amounts in the coming days.  The rainfall amounts in western El Paso County ranged between 5 and 12 inches over a 2 1/2 days time frame.  The greatest amounts occurred on the southwest side of Colorado Springs from the Broadmoor area north to near US Highway 24, where 10 to 12 inches of rain fell.  The National Weather Service in Pueblo issued a Public Information Statement regarding many of the 48-hour rainfall totals across our area of responsibility. 

Another source for information regarding specific rain amounts from around Colorado and El Paso County can be obtained from this USGS web page...

and from the CoCoRaHS web site...

Of interest to many was runoff from the Waldo Canyon burn scar. Utilizing the rain gages positioned across the burn scar, an analysis was made regarding rainfall amounts and rates. It seems remarkable that 5 to 8 inches of rain could occur on a relatively fresh, high relief burn scar, yet no catastrophic flooding resulted.  Rainfall rates were high enough to cause sustained very high, but not catastrophically high flows during Thursday, September 12th.

Last year, the National Weather Service established the criteria of 1/2 inch of rain per hour or higher for issuing a Flash Flood Warning for the Waldo Canyon burn scar.  This number looks to be in the ballpark from previous experience this summer, and during this latest episode.  Rainfall rates reached 0.80 inch per hour a number of times in a few watersheds.  The result was some overtopping of channels and life-threatening fast-flowing water.  Undoubtedly, the work done in the Waldo Canyon burn scar this season did mitigate some of the effects of the extreme rainfall amounts. 

In contrast, the three serious flash flood episodes (July 1st, July 10th, and August 9th) occurred with rainfall rates much higher than occurred with this episode; roughly 1/2 inch to 3/4 inch in a 10-minute time frame.  Rainfall rate is a very important cause to realize the effect of  serious flooding.

Here is the quick analysis of the rainfall amounts and rainfall rates for September 10th through 13th...

Extreme rainfall in the Waldo Canyon burn scar – September 10th through 13th, 2013

 

                                                9/11            9/12            3-day total

Sand Gulch                                        1.11”           3.19”           5.12”

greatest 5-minute total                        0.08”           0.11”

greatest rainfall rate                            0.32”/hr       0.51”/hr

 

 

                                                      9/11            9/12            3-day total

Upper Waldo Canyon                            1.74”           3.70”           5.98”

greatest 5-minute total                        0.15”           0.16”

greatest rainfall rate                            0.50”/hr       0.50”/hr (3 times)

 


                                                      9/11            9/12            3-day total

Lower Waldo                                     2.16”           4.45”           7.29”

greatest 5-minute total                       0.16”           0.16”

greatest rainfall rate                           0.60”/hr       0.60”/hr, 0.80”/hr (2 times)

 

          

                                                      9/11            9/12            3-day total

Upper Williams Canyon                        3.11”           4.17”           7.92”

greatest 5-minute total                       0.16”           0.31”

greatest rainfall rate                           0.80”/hr       0.80” (40 minutes)

 

 

                                                      9/11            9/12            3-day total

Upper Queens  Canyon                        2.12”           4.61”           7.52”

greatest 5-minute total                       0.12”           0.23”

greatest rainfall rate                           0.60”/hr       0.80”/hr (3 times)

 

                                                 

                                                      9/11            9/12            3-day total

Camp Creek above Glen Eyrie               2.08”           4.65”           7.36”

greatest 5-minute total                       0.11”           0.22”

greatest rainfall rate                           0.40”/hr       0.60”/hr (3 times), 0.75”/hr (2 times)

 

                                                         

 

                                                      9/11           9/12            3-day total

Douglas Creek above Flying W              1.50”           4.65”           6.78”

greatest 5-minite total                        0.20”           0.24”

greatest rainfall rate                           0.60”/hr       0.75”/hr (2 times)

 

 

                                                      9/11            9/12            3-day total

West Monument                                 1.28”           4.45”           6.64”

greatest 5-minute total                       0.11”           0.24”          

greatest rainfall rate                           0.40”/hr       0.70”/hr (2 times), 0.80”/hr

 

 

A what if…data from the Rod and Gun Meteorological Station on Fort Carson…just south of Colorado Springs.

Between 6:25 p.m. and 8:20 p.m. Thursday evening, Sept. 12th, for each 5-minute interval, rainfall rates exceeded 0.20”. 

During that time period, 7.90” of rain fell, with an average 5-minute rainfall of 0.33”. 

In one 30-minute period, 2.35” of rain fell.

In one 60-minute period, 4.40” of rain fell, and during that time frame, in a 15-minute period, 1.48” of rain fell.

Imagine if that storm would have occurred over the Waldo Canyon burn scar.

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Last updated Friday, September 13th, 3:20 p.m.



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